1. Field of the Invention
This invention relates generally to an image enhancer, and more particularly is directed to an image enhancer for a color television camera having plural solid state image sensors.
2. Description of the Prior Art
In the existing color television camera having three pick-up tubes, three primary color signals, such as green, red and blue color signals, are supplied to a matrix circuit and a luminance signal is generated therefrom, and an image enhancing signal generated from the luminance signal is added to the luminance signal. However, the image enhancing signal generated from the luminance signal is not always a correct signal representing the edge component of the image due to the misregistrations of the three pick-up tubes. And so an image enhancer in which an image enhancing signal is generated from a green primary color signal only has been proposed. Such an image enhancer is shown in FIG. 4.
In FIG. 4, numerals 31G, 31R and 31B show input terminals to which primary color signals from pick-up tubes for green, red and blue are supplied, respectively. The green signal G at the input terminal 31G is phase advanced by one horizontal scanning period as to red and blue signals which are obtained at the input terminals 31R and 31B. The green signal G is supplied to a series circuit of delay line circuits 32 and 33 of one horizontal scanning period. The input signal of the delay line circuit 32 and the output signal of the delay line circuit 33 are added together by an adder 34. The output signal of the delay line circuit 32 is supplied to one input of a subtracter 35 while the output of the adder 34 is also supplied to another input of the subtracter 35, and the vertical edge or contour component signal is generated at the output of the subtracter 35. The output signal of the subtracter 35 is supplied to a low-pass-filter 37 and the bandwidth of the signal in the horizontal direction is limited thereby. And the vertical image enhancing signal is generated at the output of the low-pass-filter 37.
The output signals of the adder 34 and the delay line circuit 32 are supplied to the adder 36. And the output signal of the adder 36 is supplied to a high-pass-filter 38 which forms twice differentiating circuit, and the horizontal image enhancing signal is obtained at the output of the high-pass-filter 38. The output signals of the low-pass-filter 37 and the high-pass-filter 38 are added together by an adder 39, and a composite image enhancing signal is generated at the output of the adder 39. The composite image enhancing signal from the adder 39 is supplied to adders 40G, 40R and 40B respectively and added to the input primary color signals. Accordingly, the image enhanced green, red and blue signals are obtained at output terminals 41G, 41R and 41B which are led out from the outputs of the adders 40G, 40R and 40B respectively.
The above image enhancer, if applied to a color television camera having three pick-up tubes, can realize a pretty good fidelity as the green signal generated from the pick-up tube has the sufficient resolution and the contribution ratio of the green signal to the luminance signal is very high.
However, if the above described image enhancer is applied to a color television camera having three solid state image sensors, such as CCD image sensors, for green, red and blue colors of an image of an object wherein the image of the object projected on the image sensor for green is displaced in the horizontal direction by half the alignment pitch of picture elements relative to the image of the object projected on the other image sensors for cancelling the sampling side band component centered by the sampling frequency when the image of the object is B/W or colored with low color saturation and for improving the resolution of the picture, the balance of the level of the sampling side band components is broken due to the image enhancing signal generated from the green signal, and so the object for improving the resolution can not be achieved.